In recent years, several configurations of optical rotation sensors have been proposed for a large variety of applications, ranging from micro-satellite systems to terrestrial vehicles.
Classical optical rotation sensors which are based on the Sagnac effect include both active configurations, such as ring laser gyroscopes (also named “gyros”) in free space optics, and passive configurations in fiber optics technology, such as Resonant Fiber Optics Gyroscopes (RFOGs) and Interferometric Fiber Optic Gyroscopes (IFOGs). IFOGs and RFOGs sensors are based on an open optical path and an optical ring resonator, respectively. The Sagnac effect causes a phase shift or frequency shift between two counter-propagating light beams being proportional to the angular velocity of the optical rotation sensor. Due to the Sagnac effect, a phase change can be detected using a phase sensitive read-out mechanism (used in IFOGs), whereas a frequency change can be detected using a frequency sensitive read-out mechanism (used in RFOGs).
The phase sensitive read-out mechanism is based on the detection of a power variation caused by the interference between the two counter-propagating light beams which experience a rotation induced phase mismatch (Sagnac phase shift). Differently, the frequency sensitive read-out mechanism is based on the detection of a difference in the resonance frequencies between two counter-propagating light beams which resonate at different wavelengths due to the rotation (Sagnac resonance wavelength difference).
In the IFOGs, a key element (which is sensitive to the angular velocity) comprises one or more optical fiber multi-turn coils. The Sagnac phase shift induced by the Sagnac effect is directly proportional to the angular velocity, the fiber coil diameter, and the number of coils. The resolution of these devices, i.e. the minimum detectable angular velocity, is inversely proportional to the total length of the optical fiber, i.e. inversely proportional to the fiber coil diameter. This means that the overall area occupied by the optical fiber coils is very large. As an example, inertial state-of-the-art IFOG systems show a resolution of 0.001°/h. Such systems are e.g. used in satellites for Earth and planet observation. However, in order to provide a resolution of 0.001°/h, four optical fiber coils having each a diameter of 20 cm and a fiber length of 5 km have to be used. In contrast, in the RFOGs, the key sensitive element comprises a resonant optical fiber cavity. The Sagnac resonance wavelength difference induced by the Sagnac effect is directly proportional to the angular velocity and strongly depends on the architecture of the resonant cavity. The resolution of the RFOGs is enhanced by increasing the length of the resonant cavity. Thus, like in IFOGs, in RFOGs the overall area occupied by the resonant cavity is large.
The following references describe known optical rotation sensor technology:    C. Ciminelli, F. Dell'Olio, C. E. Campanella, M. N. Armenise, “Photonic-technologies for angular velocity sensing”, Advances in Optics and Photonics 2, 370-404 (2010)    M. N. Armenise, V. M. N. Passaro, F. De Leonardis, M. Armenise: Modelling and Design of a Novel Miniaturized Integral Optical Sensor for Gyroscope Applications, J. Lightwave Technol., vol 19, pp. 1476-1494, 2001    C. Ciminelli, C. E. Campanella, M. N. Armenise: Optimized design of Integrated Optical Angular Velocity Sensors based on a Passive Ring Resonator, J. Lightwave Technol., vol 27, pp. 2658-2666, 2009.